1. Field of the Invention
The present invention relates to an image pickup apparatus for a digital camera or the like, a control method therefor, a control program for implementing the control method, and a storage medium storing the control program.
2. Description of the Related Art
Conventionally, there has been known a digital camera in which an optical image of a subject taken in by a taking lens is photoelectrically converted into an analog video signal by an image pickup device. Image processing is carried out on the analog video signal, thereby generating digital image data.
Generally, this kind of digital camera measures the brightness of the subject in pre-photography preparations from the video signal, and based on the measurement results, automatic exposure control processing (hereinafter referred to as “AE processing”) is carried out to obtain a suitable exposure value. Then, automatic focus detection processing (hereinafter referred to as “AF processing”) is carried out to drive a focus-adjusting lens so that the subject is focused. The subject brightness value is metered from the video signal again, and photographic exposure conditions are thereby determined.
Two kinds of AF processing methods, i.e. continuous AF processing and single AF processing, are commonly known. The continuous AF processing continuously repeats focus detection until just before photography preparations commence during operation of electronic finder function. The single AF processing carries out focus detection only once, at the time the photography preparations are instructed. Further, conventionally, two kinds of AE processing methods, i.e. feedback AE processing and scanning AE processing, are also known. The feedback AE processing carries out exposure control so as to maintain suitable brightness of a repeatedly photographed subject while determining photographic exposure conditions, whereas the scanning AE processing uses a plurality of predetermined exposure values so as to cope with any sudden changes in brightness, carries out exposure control, and determines photographic exposure conditions.
In conventional AE processing, a method has been proposed that, for the purpose of photographing with a constantly suitable exposure, carries out exposure control by selectively using the feedback control method and the scanning control method (refer to Japanese Laid-Open Patent Publication (Kokai) No. 2002-314876, for example).
However, the above-described conventional digital camera commonly omits the AE processing so that it can carry out the AF processing at the beginning of the photography preparations. When employing such a control method, however, it is impossible to cope with any sudden changes in brightness occurring just before the start of photography preparations, and thereby no suitable exposure value can be obtained.
In carrying out the continuous AF processing in particular, because more control time is allotted to the AF processing than the AE processing during operation of the electronic finder function, the AE processing control period becomes accordingly longer. Thus, there are cases where the exposure status at the beginning of photography preparations is unsuitable. Accordingly, when the continuous AF processing switches over to photography preparations, if a control method is adopted that omits the AE processing carried out during the beginning of photography preparations, photography is carried out without a suitable exposure value.